LMV604: Output goes non-linear at upper end of range

Dave Heyl

Part Number: LMV604
Other Parts Discussed in Thread: TLV9004, TLV2464, TLV2784, OPA4342, OPA4316

Number: CS1215541
Contact: David Heyl
First name: David
Last name: Heyl
Short description: Output goes non-linear at upper end of range
Phone: 15137775233
Email: dave.heyl@pe-ltd.com
Company: Performance Electronics
Company phone:
Language: English
State: Open
Provide case details or comments:

I specified the LMV604 as an alternate for an MCP6L04 op-amp that we couldn't acquire - these op-amps are used on a large number of our products. We now have the first batch of boards moving through production and boards with the LMV604 are failing our production test. The test is fairly straightforward - we input 0V, 2.5V, and 5V, and then check the output from the op-amp within a range. The circuit is simple (shown at bottom) - an RC at the input and then a voltage divider to reduce the input down to a range of 0 to 3.3V since the op-amp is powered from a 3.3V supply. When I did more detailed testing with the LMV604, the output jumps to the rail somewhere around a 4.7V input as shown below. The MCP6L04 op-amp in the same circuit is linear all the way to the rail, as shown in the second illustration below. Can you explain this? How would I have pre-determined this issue from the datasheet when I was selecting alternates? This was completely unexpected. When I was checking parameters relevant to this application, I saw that this is a rail-to-rail output. And it does go to the rail, but not in a way that is useful, in my opinion.

over 1 year ago

0 Isaac` Rose over 1 year ago

Prodigy 10 points

Viktorija Cecil, Sean Rauchfuss

0 Jacob Nogaj over 1 year ago in reply to Isaac` Rose

TI__Expert 8926 points

Hi David,

The issue exists because the LMV604 is not specified for the input common mode voltage range you are testing with.

LMV604 is specified for a common mode input range from V- to V+-1V

VS=2.7V:

The amplifier enters a nonlinear state when this specification is violated, as seen at around analog input = 4.5V.

This training video covers common mode input and output limitations for amplifiers: Input and output limitations - Common mode voltage

Solutions involve either using a device with a rail to rail input stage, or reducing the common mode range to be within datasheet specifications.

I am happy to generate an alternate device list for your application.

Are there any critical amplifier specifications for your design?

Thanks,

Jacob

0 Clemens Ladisch over 1 year ago in reply to Jacob Nogaj

Guru 257270 points

ti.com/cross-reference-search/singlepart?searchTerm=MCP6L04 suggests the TLV9004 as a drop-in replacement. It is out of stock.

Here is a search for similar quad 3.3 V rail-to-rail opamps that are available, but the search funtion does not check for availability of the package type. In TSSOP, only a few fast opamps like OPA4316, TLV2464(A), OPA4342, TLV2784 are available; you would have more luck with low-power opamps that are much slower.

0 kai klaas69 over 1 year ago

Guru 140200 points

Hi Dave,

yes, you violate the common mode input voltage range of LMV604 and the LMV604 is no input rail-to-rail OPAmp.

If you have to use the LMV604 and cannot take another OPAmp, a remedy is to modify the input voltage divider to not violate the common mode input voltage range and to add some gain to compensate for the increase of input voltage dividing.

Kai

0 Dave Heyl over 1 year ago

Prodigy 10 points

Thanks to all who replied - I appreciate the quick responses and the advice.

Regards,

Dave

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LMV604: Output goes non-linear at upper end of range